Lawyers for 53-year-old Mr Ortega have filed legal documents in relation to the charges.

In a signed document submitted in court, Mr Ortega flatly denied that he abused his step-daughter Zoilamerica Narvaez who is now aged 30.

"As to the fundamental issue, I deny, reject, contradict and impugn these charges," the statement said.

Two decades of abuse

Earlier in the week, Ms Narvaez formally charged Mr Ortega with rape, sexual assault and continual abuse from 1978 to 1998.

In a separate civil action, she petitioned to annul her 1986 adoption by Mr Ortega.

Zoilamerica Narvaez, 48-pages of accusations

Her 48-page affidavit detailed her story of unrelenting sexual and psychological abuse which went on, she says, in the name of revolution.

"He justified his conduct with the argument that I, through the sex act, gave him emotional stability," the affidavit said.

"He was making me believe that, with my sacrifice, I supported and protected the revolution."

'Case should be thrown out'

Mr Ortega's legal team has argued that the case should be thrown out on the basis of statute of limitations and other technical issues.

As a member of the National Assembly, Mr Ortega is immune from criminal prosecution, although the legislature could strip him of that protection.

But lawyers said a petition to do so should come from Ms Narvaez, who has demanded that her step-father should renounce his immunity.

Brother denounces story

Rafael Ortega, Zoilamerica Narvaez's brother has denounced her story, claiming she was being manipulated by a close friend, Sandinista dissident Henry Petrie.

Calling a news conference at the Sandinista headquarters, Rafael Ortega added a bizarre twist to the case, saying that Mr Petrie proclaimed himself an extraterrestrial with an earthly mission.

The abuse accusations have rocked the country's largest opposition party.